Often, a film-like anti-reflection structure for improving visibility is provided on the surface of a display, for example, a computer. A method for preventing reflection by closely disposing a plurality of fine prominent convex protrusions on the surface of a transparent substrate (transparent film) has been proposed as this anti-reflection structure. The so-called “moth-eye structure” principle is applied in this method. Moth-eye structures seek to prevent reflection by continuously varying the refractive index with respect to incident light in the thickness direction of the substrate, thereby eliminating a discontinuous interfaces of the refractive index.
Such an anti-reflection structure can realize high anti-reflective performance, provided that the refractive index with respect to incident light can be continuously varied. As such, in principle, anti-reflection structures are not limited to fine prominent convex protrusions and may also be a structure that is configured with fine concavities.
Anti-reflective performance of an anti-reflective structure may be superior if refractive index change is more gradual. Therefore, it is preferable that a ratio of height or depth of the fine prominent convex protrusions or concavities to a width of the structure (hereinafter referred to as the “aspect ratio”) be high.
On the other hand, with higher aspect ratios, a fine convexity or concavity is structurally fragile, leading to difficulty in maintaining the shape of the structure. There is also a problem in that higher aspect ratios lead to increased complications when fabricating the structure. For example, these types of fine shapes can be fabricated by nanoimprinting or other methods in which a mold is used. However, there is a problem in that, when the aspect ratio is high, the mold becomes clogged with resin or the like when transferring the prominent convex protrusions or concavities from the mold.
As such, many lines of research are being pursued to obtain high anti-reflective performance without increasing the aspect ratio.
In Patent Document 1, it is described that strong coloration in reflection may be reduced while a ratio of high aspect prominent convex protrusions within a concavo-convex structure can be reduced by imparting a certain degree of variation to the height of prominent convex protrusions of the concavo-convex structure.
Additional problem for an anti-reflective structural body having fine prominent convex protrusions and concavities is deposition of a fine foreign object between the prominent convex protrusions or in the concavities, which may impair the anti-reflective effect.
Patent Document 2 describes a structural body having fine concavities and prominent convex protrusions resistant to water deposits achieved by large water contact angle of 140° or greater at a surface of the fine concavities and prominent convex protrusions.